Fire resistant particle board containing monobasic ammonium phosphate and/or ammonium sulphate



United States Patent FHRE RESISTANT PARTICLE BOARD CONTAINING MON OBASI'C AMMONIUM PHOSPHATE AND/0R AMMONIUM SULPHATE Earland G. Hallonquist, Nanaimo, British Columbia, John M. Jaworsky, New Westminster, British Columbia, and Victor G. Kassay, Vancouver, British Columbia, Canada, assignors to MacMillan, Bloedel Limited, a corporation of British Columbia No Drawing. Filed Feb. 17, 1964, Ser. No. 345,077

11 Claims. (Cl. 26017.3)

ABSTRACT OF THE DISCLOSURE A fire resistant particle board made-up of wood particles, a resin binder, and one or more fire-retardant salts mixed together and pressed under heat to produce a board of a desired density, and the method of making this board.

This invention relates to a fire resistant particle 'board and a method of making this board.

An object of the present invention is the provision of a fire resistant particle board which is practically no more expensive than an ordinary particle board, retains the usual particle board strength, and is easy and cheap to manufacture.

Another object is the provision of a method of making particle board fire resistant during the manufacture of the board without materially increasing the cost thereof and without sacrificing any strength of the board.

The term wood particles as used throughout this specification and in the appended claims is intended to include particles, chips, shavings, flakes, strands and the like of the type used in the manufacture of particle board and flake boards.

The conventional method of imparting fire resistance to wood products is by vacuum-pressure impregnation with aqueous solutions of fire-retarding chemicals. This method is expensive and time consuming, involving expensive equipment, and additional drying and sanding steps.

A fire resistant board according to the present invention comprises wood particles pressed together and bonded with urea formaldehyde resins, and a salt mixed throughout the particles and resin, said salt being monobasic ammonium phosphate and/or ammonium sulphate. The salt is added to the wood particle furnish used to make the boards prior to the hot pressing step during the manufacture thereof. This can be done without any special equipment, and it eliminates the time consuming and expensive vacuum-pressure fire retarding treatment of the finished boards, as well as extra redrying and sanding steps. These salts, when added to the wood particle furnish in amounts required to give fire retardancy, do not reduce appreciably the bonding properties of the urea-formaldehyde resin used to bond the particles together in the board.

The salts can be added as dry crystals or powder, as a water spray, or by dip treatment of the wood particles. Of these, the most practical and inexpensive method of addition is in the dry form, and very good results have been obtained by this means. Amounts ranging from about 5% to about 15% of the wood furnish can be used, but very low amounts do not give the maximum fire resistance, and amounts in the upper range begin to cause lossof strength properties, and are more costly. It has been found that amounts of about of the salt on the dry weight of the wood furnish are adequate to give good fire retardancy, and do not cause any appreciable loss of bond strength.

The mixture of wood particles, urea formaldehyde resin and salt is pressed into a board at temperatures ranging from about 275 F. to about 350 F. and pressures ranging from about 200 to about 400 p.s.i. over a period of from about 4 minutes to about 10 minutes.

The following are examples of methods of producing fire resistant board according to this invention.

EXAMPLE I A mixture of cedar shingle hay, splints and sawdust was broken down in a shredder, passed through a disc refiner, and dried. The mixture comprised particles ranging in size from those passing through about a 5 mesh (Tyler) standard screen to those retained on about a 30 mesh screen. Petroleum wax (45% water emulsion) in an amount of 1.25% (dry basis) on the dry weight of the wood, was sprayed on the wood particles in a tumbling drum mixer. This was followed by a further spray application of urea formaldehyde resin in an amount of 6% (dry basis) on the weight of the dry wood. To this mixture of wood particles, urea resin and petroleum wax was added 10% of dry monobasic ammonium phosphate on the dry weight of the wood, and this salt was mixed thoroughly with the other constituents.

The wood particle-salt-resin-wax furnish was directed onto a metal caul by a forming apparatus to give an even mat. A sufiicient mat thickness was used to give a inch thick finished board at 0.7 density after hot pressing. Another caul was laid on the top of the mat. Water had been previous sprayed on the inner caul surfaces (5 to 15 gms. per sq. ft.) to provide a rapid pressing cycle and to harden the board surfaces. The mat, with cauls on each side, was placed in a hydraulic hot press, and pressed at 330 F. as follows: The maximum pressure (400 p.s.i.) was applied for 1 /2 minutes to compress to the desired thickness (controlled by stops). The pressure was then reduced over a period of /2 minute to 50 p.s.i., held at 50 p.s.i. for /2 minute, and then over a period of 1 /2 minutes reduced to zero. The total pressing time was thus 4 minutes.

The board prepared in this way was tested for physical properties and fire resistance in comparison with a similar thickness and density board prepared in the same manner, but without the addition of the monobasic ammonium phosphate. Results were as follows:

Fire Standard Resistant Board Board Fire Test} Loss of weight, percent 28 83 Fire Test, Max. Burning Temp. F. 615 1, 375 Modulus of Rupture, p.s.i 2, 873 2, 950 Internal Bond, p.s.i 82 83 1 The fire test was carried out with the fire-tube apparatus described in ASTM standards E; 69-50 (Combustible Properties of Treated Wood by Fire-Tube Apparatus), and according to the described procedure of this test.

EXAMPLE II inch board of 0.70 specific gravity, bonded with urea formaldehyde resin was prepared in a manner similar to Example I, but in this case 10% of ammonium sulphate on the weight of the dry wood furnish was used as the fire retardant salt. Test results were as follows:

1 The fire test was carried out with the fire-tube apparatus described in ASTM Standards E; 6950 Combustible Properties of Treated Wood lines-Tube Apparatus, and according to the described procedure of s es 3 EXAMPLE III A standard particle board which was treated with a standard commercial fire retardant by a conventional vacuum-pressure impregnation treatment had a fire test 5. A fire resistant particle board according to claim 4 containing at least about 10% by weight of said salt.

6. A fire resistant particle board according to claim 4 containing about 6% by Weight, based on the dry weight weight loss of 24% and a maximum burning temperature the wood particles of said urea'formaldehyde resin of 475 F., but only a modulus of rupture of 900 p.s.i. bmdeg fi This indicates that the vacuum-pressure treatment and 1 re.reslstant Pamela Poard conslstmg essennany subsequent redrying lowers the strength of the particle o a purahty of .Wood parades pressed i and board Very drastically bonded together w th a urea-formaldehyde resin binder, Further tables illustrating the useful minimum and 10 3:? fi g a i i f fi z maximum percentages of salt which can be used in the f g on e ry E 3 g p fire resistant particle board of this invention are as folo .mono i gmmomum p osp sa S t bemg lows: uniformly dlstrlbuted throughout said particle board.

TABLE I [Using Monobasic Ammonium Phosphate] Fire Test Amount of Salt Modulus of Internal on dry Wt. of wood Loss of Maximum Rupture, Bond,

Wt., Burning p.s.i. p.s.i. percent Temp, F.

See footnote bottom of Table II.

TABLE II [Using Ammonium Sulphate] Fire Test Amount of Salt Modulus of Internal on dry Wt. of wood Loss of Maximum Rupture, Bond,

. Burning p.s.i. p.s.i.

Temp., F.

to the described procedure of this test.

What we claim as our invention is:

1. A fire resistant board comprising wood particles pressed together and bonded with about 6% (dry basis) of the weight of the wood particles of urea-formaldehyde resin, and about 10% of the dry wood weight of a salt mixed throughout the particles and resin, and salt being selected from the group consisting of monobasic ammonium phosphate and ammonium sulphate.

2. A fire resistant board comprising wood particles pressed together and bonded with about 6% (dry basis) of weight of wood particles of urea-formaldehyde resin, and from about 5 to 15% of the dry weight of the wood particles of a salt mixed throughout said particles and resin, said salt being selected from the group consisting of monobasic ammonium phosphate and ammonium sulphate.

3. The method of making fire resistant board which comprises thoroughly mixing wood particles, a salt and urea-formaldehyde resin and petroleum wax, said salt being selected from the group consisting of monobasic ammonium phosphate and ammonium sulphate and being about 5 to 15% of the dry weight of the wood particles said resin being about 6% (dry basis) of the dry wood weight, and pressing the mixture into a board at temperatures ranging from about 275 F. to about 350 F. and pressures ranging from about 200 to about 400 p.s.i. over a period of from about 4 minutes to about 10 minutes.

4 A fire resistant particle board comprising a plurality of wood particles pressed together and bonded together with urea-formaldehyde resin binder, said board containtaining from about 5 to about 15% by weight based on the dry weight of the wood particles, of monobasic ammonium phosphate salt, said salt being uniformly distributed throughout said particle board.

8. A fire resistantant particle board according to claim 7 containing at least about 10% by weight of said salt.

9. A fire resistant particle board according to claim 7 containing about 6% by weight, based on the dry weight of the wood particles, of said urea-formaldehyde resin binder.

10. A method of making fire resistant particle board which comprises the steps of thoroughly mixing together a plurality of wood particles, urea-formaldehyde resin binder, petroleum wax, and from about 5 to about 15 by weight, based on the dry weight of the wood particles, of monobasic ammonium phosphate, and pressing the mixture at a temperature of from about 275 to about 350 F. and a pressure of from about 200 to about 400 p.s.i. for about 4 to about 10 minutes to form a particle board.

11. A method according to claim 10 wherein said mixture consists essentially of a plurality of wood particles, urea-formaldehyde resin binder, petroleum wax, and from about 5 to about 15% by weight, based on the dry weight of said wood particles, of monobasic ammonium phosphate.

References Cited UNITED STATES PATENTS 2,452,054 10/1948 Jones et al. 260 2,658,878 11/1953 Sears 260l7.3 2,859,187 11/1958 Ropella 161-262 2,962,459 11/1960 Ash et al 26017.2 3,160,596 12/1964 Spencer 260-173 WILLIAM H. SHORT, Primary Examiner.

E. M. WOODBERRY, Assistant Examiner. 

